When serious consideration is given to structural simplification, weight reduction, or cost reduction of a device driven by an engine, a fuel injection system, ignition system, etc., is operated without a battery using a generator driven by the engine as the power supply. In the present specification, a fuel injection system operated without a battery and using a generator driven by the engine as the power supply is called a battery-less fuel injection system. This type of fuel injection system is disclosed in Japanese Laid-Open Patent Application No. 2005-330815 and Japanese Laid-Open Patent Application No. 2002-89390.
To have an engine to which fuel is supplied by a fuel injection system perform a desired operation, it is necessary to control the fuel injection timing and the fuel injection amount, and control the ignition timing of the engine. Normally, these controls are performed by an electronic control unit (ECU) provided with a CPU for executing software needed for control, and with circuits for driving the fuel injection system and/or the ignition system according to commands given from the CPU.
The voltage outputted by the generator attached to the engine is converted to power supply voltage (e.g., 5V) given to the ECU, and power supply voltage (e.g., 12V), given to the fuel pump and the injector by a power supply circuit provided with a rectifier circuit, and with a control circuit for controlling the output of the rectifier circuit to a fixed value or less.
An engine for driving a vehicle, etc., without a battery mounted is started by a manually operated starting device such as a recoil starter or a kick starter. When the engine starting operation is performed, the generator generates voltage, and power supply voltage is given to the fuel pump and the ECU through a predetermined power supply circuit from the generator. When the output voltage of the generator reaches the voltage at which the ECU can operate, the ECU microprocessor is activated.
Because power supply voltage is also given to the fuel pump in such instances, the fuel pump starts operating, and the fuel inside the fuel tank is supplied to the injector. After a reset operation of the ECU is completed, the ECU gives an injection command pulse to an injector drive circuit and has the injector perform the injection operation when it has been detected that a crank angle sensor attached to the engine has generated a crank angle signal at a set reference rotation angle position.
When the engine is started to which fuel is supplied by a battery-less fuel injection system, the initial explosion of the engine after the start of the starting operation is thus performed as early as possible, and to make it easy to start the engine, the ECU has the injector perform the injection operation when the crank angle signal generated by the crank angle sensor is detected, without waiting for the regular fuel injection timing to be detected. When the engine has two or more cylinders, and an injector is provided for each cylinder, the injection operation is performed simultaneously for all the injectors when the crank angle signal is detected, in order to have the initial explosion performed as early as possible by one of the cylinders after the starting operation starts.
The ECU also controls the ignition system for igniting the engine, and has the ignition system perform the ignition operation at a predetermined rotation angle position. When the ignition operation is performed on a cylinder of an engine to which fuel injected from an injector has been supplied, the first combustion (initial explosion) is performed at that cylinder, and the engine is started.
To have combustion performed within a given cylinder of the engine when the cylinder is ignited, it is necessary to have injected sufficient fuel to inside the intake pipe, or inside the cylinder, etc., in an amount necessary for the air-fuel ratio of the air fuel mixture that exists inside that cylinder at the time of ignition to be a value within a range over which combustion is possible. The amount of fuel injected from the injector is determined by the product of the pressure of the fuel given from the fuel pump to the injector (fuel pressure), and the time the injector valve is open (valve opening time or fuel injection time). Therefore, after starting of the starting operation, until the first fuel injection is performed, it is necessary to raise the fuel pressure given to the injector to a predetermined pressure to have the engine started reliably.
In the battery-less fuel injection system, within the small amount of time in which starting operation is performed to start the engine, it is necessary to drive the fuel pump with output of the generator driven by the engine, and increase the fuel pressure given to the injector to a predetermined pressure. When the fuel injection operation is performed by the injector in a state with insufficient fuel pressure, it is not possible to inject sufficiently atomized fuel from the injector, so fuel of a large particle diameter is injected inside the engine intake pipe or inside the cylinder (combustion chamber interior). When large particle diameter fuel is injected, it is difficult for the fuel to be sufficiently vaporized; therefore, it is no longer possible to obtain an air fuel mixture of the predetermined air-fuel ratio, and engine startability significantly decreases. Especially when the engine is started at low temperatures, due to a decrease in the viscosity of the engine lubricating oil, there is a marked increase in the burden on the driver for starting operation, and since the crankshaft cannot rotate with sufficient speed, it is difficult to raise the generator output voltage by the starting operation, and such problems become more prominent. In the worst case, due to the inflow of fuel inside the cylinder without sufficient vaporization, there are cases when the periphery of the spark plug discharge electrode becomes wet, and no sparking will occur, making it impossible to start the engine despite repeating the starting operation many times.
In a battery-less fuel injection system, in order to prevent the occurrence of a situation with insufficient fuel pressure when the engine is started, with the invention noted in Japanese Laid-Open Patent Application No. 2005-330815, a mechanically driven fuel pump to supply the fuel inside the fuel tank to the injector is provided in addition to an electric fuel pump driven by the output of the generator. The mechanical driving force for driving the mechanically driven fuel pump is given from the starting device, and the fuel pressure given to the injector is increased by driving the mechanically driven fuel pump during starting operation.
Also, Japanese Laid-Open Patent Application No. 2002-89390 discloses an invention with which a fuel pressurization device is inserted midway in a fuel supply passage that reaches from the fuel pump to the injector, and insufficient fuel pressure during starting is prevented by using this pressurization device to raise the pressure of the fuel given to the injector. There are disclosed, as fuel pressurization devices, a device that operates in conjunction with the recoil starter to increase the fuel pressure, and a device that increases the fuel pressure in advance by manual pulling of an operation knob before starting the engine starting operation.
According to the invention noted in Japanese Laid-Open Patent Application No. 2005-330815, when the engine is started, it is necessary to drive the mechanically driven fuel pump simultaneously with driving the kick starter or the recoil starter, so there is a greater burden on the driver, and the problem of difficulty in increasing the rotating speed of the crankshaft arises. If the crankshaft cannot be rotated at sufficient speed, there can be no great expectation of an effect in terms of increasing the fuel pressure, despite the addition of the mechanically driven fuel pump. Especially when the engine is started in the cold, the burden on the starting device increases due to a decrease in the viscosity of the engine lubricating oil, and because it is difficult to rotate the crankshaft at sufficient speed, it is also difficult to sufficiently increase the fuel pressure, despite provision of the mechanically drive fuel pump.
Also, according to the invention disclosed in Japanese Laid-Open Patent Application No. 2002-89390, the burden on the manual starting device is greater, so the same problems as noted above arise. Japanese Laid-Open Patent Application No. 2002-89390 discloses increasing of the fuel pressure by pulling the knob of the fuel pressurization device before starting the starting operation, but in such a configuration, separate operations for the starting device and the fuel pressurization device must be performed when the engine is started, inevitably complicating the starting operation.
Also, according to the invention disclosed in Japanese Laid-Open Patent Application No. 2005-330815, and according to the invention disclosed in Japanese Laid-Open Patent Application No. 2002-89390, it is necessary to provide a mechanically driven fuel pump or a fuel pressurization device in addition to the conventionally used manually operated starting device, leading to problems regarding an increase in the size and weight of the engine as well as the cost.
Furthermore, when the mechanically driven fuel pump disclosed in Japanese Laid-Open Patent Application No. 2005-330815, or the fuel pressurization device disclosed in Japanese Laid-Open Patent Application No. 2002-89390 is provided, due to extra mechanical parts being inserted in the fuel flow channel that reaches from the fuel pump to the injector, the fuel circulation efficiency decreases, so it is necessary to use a larger electric fuel pump with higher pump performance. When a large electric pump is used, not only do costs increase, but the burden on the generator increases, so it is necessary to prepare a larger generator attached to the engine than that required conventionally, leading to an increase in engine size. Also, when using a larger generator than in the past, the burden on the starter increases, making a decrease in engine startability unavoidable.
It is an object of the present invention to provide a battery-less fuel injection system that can prevent the incidence of large-particle-diameter fuel being repeatedly injected from the injector due to insufficient fuel pressure and of engine starting becoming more difficult, without adding extra mechanical parts such as a mechanically driven fuel pump, a fuel pressurization device, etc.